Sublethal Effects of Ethanol Extract of Ocimum sanctum on Laboratory Bred Population of Dengue Mosquito Aedes aegypti L. (Diptera: Culicidae)

Abstract

Objectives: Aedes aegypti is a vector of several diseases which cause serious discomfort and fatality to human being. Current investigations were carried out to assess sublethal effects of ethanol extract of the leaves of Ocimum sanctum against A. aegypti in order to find ecofriendly alternatives for integrated vector management‟. Methods: Lethal and sublethal effects of ethanol extract of O. sanctum against fourth instar larvae were assessed by using WHO protocol. The studies were extended to evaluate the effects of the extract on growth and development of the treated larvae. The chemical components present in the extracts were analyzed by Gas chromatography and mass spectroscopy (GC-MS). Results: Exposure of fourth instar larvae of A. aegypti revealed moderate toxicity. However, the treated larvae exhibited mortality during subsequent days of exposure. The treatment with the extract also has adverse impact on growth and development of the larvae. Consequently there was increase in the larval duration in the treated larvae. Larva-pupa intermediate and pupa-adult intermediate were the developmental anomalies observed in the treated fourth instar larvae. This suggested presence of juvenile hormone mimic or juvenile analogue activity in the ethanol extract of O. sanctum leaves. Presence of farnasene, a derivates of the intermediates in the juvenile hormone biosynthesis was reported in the GCMS analysis of the extract. Conclusion: Our studied indicated moderate lethal and efficient sublethal effects of ethanol extract of O. sanctum against A.aegypti. The bioactive compounds present in the extract, individually or synergistically may be used in formulating a strategy for the mosquito management